I also want to cast shadows on a transparent surface. I am using the same method, applying the mat_none material to my model. I have a duplicate of the model in the same place which has the transparency I want. The problem is that the "invisible surface" blocks the view of my object when it penetrates the surface as seen in the bottom picture and the small inset picture:




The arm moves around with bones and is one model. The red ball is a separate model that is always placed at the tip of the finger using vec_for_bone. I had to add dummy vertices to the ball so it would not get clipped (this is simalr to a method i used to make an out of view object cast a shadow into the view explained here ). I have dummy vertices in the arm (upperbody) model, but they do not seem to help. I split up the upper and lower body to get the legs to show up under the surface. Without doing that I got this result:



Any ideas how to get the hand to be visible through the transparent surface?